Semiconductor optical waveguide. method for manufacturing the same, and optical communication device using the same

ABSTRACT

It is difficult to actualize a semiconductor optical waveguide having desired properties that reflect design even when process technology for a semiconductor electronic circuit is applied as is to the production of a semiconductor optical waveguide. 
     The present invention includes: a substrate; a semiconductor optical waveguide structure arranged on the substrate; a planar region formed around the semiconductor optical waveguide structure on the substrate; and a semiconductor dummy structure that is arranged around the planar region on the substrate and is formed of a plurality of dummy patterns, wherein the semiconductor optical waveguide structure includes a line-symmetric pattern on a plane that is parallel to the substrate; and the plurality of dummy patterns are arranged symmetrically with respect to the symmetry axis of the line-symmetric pattern.

TECHNICAL FIELD

The present invention relates to a semiconductor optical waveguide, amethod for manufacturing the semiconductor optical waveguide, and anoptical communication device using the semiconductor optical waveguide.In particular, the present invention relates to a semiconductor opticalwaveguide in which a semiconductor thin film is used in an opticalwaveguide, a method for manufacturing the semiconductor opticalwaveguide, and an optical communication device using the semiconductoroptical waveguide.

BACKGROUND ART

Larger-capacity and longer-distance optical fiber communication hasprogressed due to technologies such as high-speed intensity modulationsignals and wavelength multiplexing. In addition to the technologies, inrecent years, technologies such as polarized light multiplexing andmulti-level phase modulation have been used due to the improvement ofdigital signal processing technology. In addition, communicationcapacities have been able to be still more increased utilizing existingoptical fiber networks.

Such circumstances have caused demands for the higher integration,downsizing, higher functions, lower costs, and the like of opticalcommunication devices used in optical fiber communication. There havebeen trade-off relationships between the demands, and it has beendifficult to satisfy the demands in line with the conventionaltechnologies.

The size, performance, and the like of an optical communication devicedepend greatly on the configuration and performance of an opticalwaveguide included in the optical communication device. Thus, productionof optical waveguides has proceeded using manufacturing processes forsemiconductor integrated circuits. Specifically, an optical waveguide isproduced by designing fine optical waveguide patterns on a semiconductorthin film. Semiconductors, e.g., silicon and the like, have higherrefractive indices than glass, and therefore, facilitate the downsizingof optical waveguides in comparison with glass waveguides. Further, theutilization and conversion of high-definition complementary metal oxidesemiconductor (CMOS) process technology used in manufacturing of largescale integrations (LSIs) can be expected.

An example of such semiconductor (silicon) optical waveguides isdescribed in each of PTLs 1 to 3, and the like. A silicon opticalwaveguide according to PTL 1 includes: a substrate including aninsulator such as glass; a flat-shaped silicon thin film referred to asa base; and a rectangular waveguide including silicon and having arectangular shape. The shape of the silicon optical waveguide isdesigned so that a predetermined relational expression between the widthof the rectangular waveguide, a height upward from the substrate, andthe thickness of the flat-shaped silicon thin film holds. As a result,the wavelength shift between TE and TM of guided light propagatingthrough the silicon optical waveguide can be allowed to be less than 0.2nm.

CITATION LIST Patent Literature

[PTL 1] Japanese Patent Laid-Open No. 2006-11443

[PTL 2] Japanese Patent Laid-Open No. 2000-91319

[PTL 3] Japanese Patent Laid-Open No. 2003-156642

SUMMARY OF INVENTION Technical Problem

However, the silicon optical waveguide according to PTL 1 has thefollowing problem. First, points of concern in the production of thesilicon optical waveguide will be described. In the silicon opticalwaveguide formed of silicon which is a material having a high refractiveindex, the field distribution in a propagation mode is very small incomparison with a glass waveguide formed of silica glass or the like,and therefore, the propagation mode changes sensitively with respect tothe change of a core shape. As a result, high processing accuracy isrequired in comparison with the case of forming the optical waveguide byglass-forming technology. Specifically, with regard to the requiredpattern processing accuracy of the core width of an optical waveguide,the required processing accuracy of the glass waveguide is ±0.1 μmwhereas the required processing accuracy of the silicon waveguide is±several nanometers and is higher by two orders.

Furthermore, in the pattern processing of the optical waveguide, aregion in which needed processing accuracy is required widely exists aswell as being local. Specifically, a region in which needed processingaccuracy is required, for example, such as a pattern in the vicinity ofa gate, is local in a MOS transistor, whereas the region extends overthe whole optical waveguide pattern in the optical waveguide. In otherwords, the high processing accuracy of a core width is required for anoptical waveguide pattern that has a length of several tens ofmicrometers to several hundreds of micrometers, or that in some cases,is continuous in millimeter units.

In the case of requiring phase control over the whole optical waveguidepattern, polarization dependability or phase control with higheraccuracy, and the like, the pattern processing accuracy of the corewidth of the optical waveguide is problematic. In other words, in theconfiguration of the silicon optical waveguide according to PTL 1, thephase of guided light propagating through the optical waveguide deviatesfrom a designed value due to the occurrence of a deviation orfluctuation in optical waveguide core width in a manufacturing process.

There has been such a problem as described above that it is difficult toactualize a semiconductor optical waveguide having desired propertiesthat reflect design even when process technology for a semiconductorelectronic circuit is applied as is to the production of a semiconductoroptical waveguide. In PTL 3, which proposes a designing method fordetermining a pattern for actualizing a photonic crystal waveguide, theoccurrence of a deviation from a designed value in a manufacturingprocess is not supposed.

An object of the present invention is to provide: a semiconductoroptical waveguide having desired properties that reflect design evenwhen process technology for a semiconductor electronic circuit isapplied as is to the production of a semiconductor optical waveguide; amethod for manufacturing the semiconductor optical waveguide; and anoptical communication device using the semiconductor optical waveguide.

Solution to Problem

A semiconductor optical waveguide of the present invention includes: asubstrate; a semiconductor optical waveguide structure arranged on thesubstrate; a planar region formed around the semiconductor opticalwaveguide structure on the substrate; and a semiconductor dummystructure that is arranged around the planar region on the substrate andis formed of a plurality of dummy patterns, wherein the semiconductoroptical waveguide structure includes a line-symmetric pattern on a planethat is parallel to the substrate; and the plurality of dummy patternsare arranged symmetrically with respect to a symmetry axis of theline-symmetric pattern.

An optical communication device of the present invention includes thesemiconductor optical waveguide described above.

A method for manufacturing a semiconductor optical waveguide of thepresent invention includes: arranging a first clad layer and a corelayer on a substrate; forming a core pattern by subjecting the corelayer to photolithography and etching using a predetermined mask; andarranging a second clad layer on the formed core pattern, wherein themask is formed by: periodically arranging a plurality of dummy patterns;removing a dummy pattern in a safety distance range with a predeterminedcentral axis as a center; rearranging a dummy pattern in a controlregion that is adjacent to an outside of the safety distance rangeline-symmetrically with respect to the central axis; and forming anoptical waveguide structure pattern in the safety distance range in sucha way that the central axis and a central line of the optical waveguidestructure pattern coincide with each other.

Advantageous Effects of Invention

In accordance with the present invention, there can be provided: asemiconductor optical waveguide having desired properties that reflectdesign even when process technology for a semiconductor electroniccircuit is applied as is to the production of a semiconductor opticalwaveguide; a method for manufacturing the semiconductor opticalwaveguide; and an optical communication device using the semiconductoroptical waveguide.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a plan view of a semiconductor optical waveguide according toa first exemplary embodiment of the present invention.

FIG. 1B is a cross-sectional view of the semiconductor optical waveguideaccording to the first exemplary embodiment of the present invention.

FIG. 2 is a plan view illustrating the configuration of a semiconductoroptical waveguide according to a second exemplary embodiment of thepresent invention.

FIG. 3 is a plan view illustrating the configuration of a semiconductoroptical waveguide according to a third exemplary embodiment of thepresent invention.

FIG. 4 is a plan view illustrating the configuration of a semiconductoroptical waveguide according to a fourth exemplary embodiment of thepresent invention.

FIG. 5A is a plan view illustrating the configuration of a semiconductoroptical waveguide according to a fifth exemplary embodiment of thepresent invention.

FIG. 5B is a cross-sectional view illustrating the configuration of thesemiconductor optical waveguide according to the fifth exemplaryembodiment of the present invention.

FIG. 6A is a plan view illustrating the configuration of a relatedsemiconductor optical waveguide.

FIG. 6B is a cross-sectional view illustrating the configuration of therelated semiconductor optical waveguide.

FIG. 7A is a plan view illustrating the configuration of another relatedsemiconductor optical waveguide.

FIG. 7B is a cross-sectional view illustrating the configuration of theother related semiconductor optical waveguide.

DESCRIPTION OF EMBODIMENTS First Exemplary Embodiment

FIG. 1A is a plan view of a semiconductor optical waveguide according toa first exemplary embodiment of the present invention, and FIG. 1B is across-sectional view of the semiconductor optical waveguide. As anexample of a semiconductor, the case of using silicon will be described.An upper silicon oxide layer 13 is layered on a silicon-on-insulator(SOI) substrate including a silicon substrate 10, a lower silicon oxidelayer 11, and a silicon layer 12. A core 20 which is the core pattern ofa silicon optical waveguide structure 40, and lattice-shaped dummystructures 31 are formed in the silicon layer 12.

The silicon optical waveguide structure 40 is a ridge optical waveguideof which the propagation layer is formed of a slab 21 having a smallsilicon film thickness and a flat shape, and the core 20 having a largesilicon film thickness and a small width. In the cross-sectional view ofFIG. 1B taken along the line A-A′ of FIG. 1A, the projection shape ofthe ridge optical waveguide appears in the cross sections of portions ofthe core 20 and the slab 21.

The dummy structures 31 include a plurality of dummy patterns which havea thickness generally equal to the thickness of the core 20, and throughwhich guided light does not propagate. The individual dummy patternsforming the dummy structures 31 are uniformly disposed in a wafersurface, and for example, are arranged at generally equal spacings in alattice shape (continuous line portions of FIG. 1A). In other words, thedummy structures 31 include periodic structures. Among the individualdummy patterns forming the dummy structures 31, dummy patterns inpredetermined ranges in regions in the vicinities of the core of theoptical waveguide are removed in such a way as not to affect guidedlight propagating through the optical waveguide. The broken lineportions of FIG. 1A are the removal traces 34 of the removed dummypatterns.

Subsequently, the action of the ridge silicon optical waveguide will bedescribed. Guided light is confined in the core 20, and propagatesthrough the core 20. In the ridge optical waveguide, the confinement ofguided light in the cross section of the optical waveguide in a verticaldirection is achieved by the silicon oxide layers 11 and 13 which areclad layers. Further, the confinement of light in the cross section ofthe optical waveguide in a horizontal direction is achieved by theprojection shape formed of the core 20 and the slab 21. As describedabove, the propagation mode of guided light depends on the projectionshape of the ridge optical waveguide.

In the design of an optical waveguide, the optical waveguide is commonlydesigned as a single mode waveguide with one propagation mode. Forexample, when the ridge optical waveguide has a projection shape havinga height of 1.5 μm, a ridge width of 1.2 μm, and a slab thickness of 0.5μm, the ridge optical waveguide functions as an optical waveguide forsingle-mode propagation. Guided light can be sufficiently confined in anoptical waveguide in such a single-mode condition, and a large portionof the field distribution of the guided light is in the vicinity of theridge of a core. It is sufficient to estimate the spread of the fielddistribution in the cross section of an optical waveguide core to bearound 6 μm in full width. A range in which the field distributionspreads (hereinafter referred to as “safety distance range”) is an indexfor determining whether or not to be the predetermined range in whichthe dummy patterns are removed.

Among the individual dummy patterns forming the dummy structures 31,dummy patterns located in the safety distance range are removed to beinhibited from affecting guided light propagating through the opticalwaveguide. In contrast, dummy patterns are arranged at positions apartfrom the safety distance range. In this exemplary embodiment, thepattern densities and etching areas of the dummy patterns arerespectively designed to be constant values as much as possible.

The shapes of the individual dummy patterns forming the dummy structures31 are designed, for example, to be rectangular shapes. For example, thelattice-shaped dummy structures 31 are formed by periodically arrangingthe plurality of dummy patterns. The shapes of the individual dummypatterns forming the dummy structures 31 are not limited to rectangularshapes but may be optional shapes such as circular and polygonal shapes.

It should be noted that the dummy structures including the plurality ofdummy patterns are arranged line-symmetrically with respect to thecentral line of the optical waveguide core (hereinafter referred to as“core central line”). The reason for this is that local etchingconditions in the vicinity of the waveguide core can be uniformalized byarranging the dummy structures symmetrically with respect to the opticalwaveguide core. For example, it is desirable to maintain the symmetry ofthe arrangement of the dummy structures with respect to the opticalwaveguide core in, at least, a region of 10 μm to 100 μm from the corecentral line. In contrast, it is not necessary that a region in wherethe need for controlling the phase of guided light with high accuracy islow has the symmetry of the arrangement of the dummy structures withrespect to the optical waveguide core. In the region, the individualdummy patterns forming the dummy structures may be arranged in such away as to have a uniform overall pattern density.

As described above, the plurality of dummy patterns forming the dummystructures are arranged in the region excluding the region in which theprojection shape of the core of the ridge optical waveguide is formed,and the safety distance range, in the case of designing an opticalwaveguide pattern. In this case, the plurality of dummy patterns arearranged line-symmetrically with respect to the core central line. Forexample, the dummy patterns having the shape of a square with a side of10 μm are arranged at an equal pitch of 15 μm. The shapes of theindividual dummy patterns forming the dummy structures may be determineddepending on a manufacturing process used, for example, such as a dryetching apparatus using plasma and etching gas.

Next, a method for manufacturing the semiconductor optical waveguidedescribed above will be described. A photomask used in aphotolithography step for etching processing of a semiconductor corelayer is formed based on the design of waveguide patterns including thedummy patterns described above. First, photomask data in which aplurality of dummy patterns are periodically arranged on the wholesurface is created. Then, in a region in which a waveguide core patternis arranged, dummy patterns in a safety distance range with a corecentral line as a center are removed from the photomask data.Furthermore, in a waveguide pattern region in which the width of thewaveguide is intended to be precisely controlled, for example, in aregion that is at not less than a safety distance from the core centralline and is 10 μm to 100 μm from the core central line, the plurality ofalready arranged dummy patterns are removed from the photomask data.Then, a plurality of dummy patterns are newly arranged in the region ofthe photomask data in such a way as to be line-symmetrical with respectto the core central line. Finally, the waveguide core pattern and thedummy patterns are synthesized on the same photomask data. An etchingmask is formed on a substrate in the photolithography step using thephotomask produced using the photomask data prepared as described above,and the etching processing and the like of the substrate are performed,thereby producing the optical waveguide.

Specifically, a first clad layer (for example, SiO₂ layer) and a corelayer (for example, Si layer) are arranged on the substrate, a corepattern is formed on the core layer through the photolithography stepusing the photomask described above and the etching step, and a secondclad layer (for example, SiO₂ layer) is arranged on the formed corepattern, thereby producing the optical waveguide according to thisexemplary embodiment. When a plurality of optical waveguides wereprototyped using the mask pattern formed as described above, it wasconfirmed that the deviations of their optical phases and the like fromdesigned values were small, and their desired properties were able to beachieved.

The configuration of the semiconductor optical waveguide described aboveand the method for manufacturing the semiconductor optical waveguideenable the suppression of the occurrence of a deviation and fluctuationin the width of an optical waveguide core in an etching process which isone of processes for manufacturing the optical waveguide core, and theformation of the width of the optical waveguide with high accuracy. As aresult, the semiconductor optical waveguide having desired propertiescan be uniformly actualized using a process for manufacturing asemiconductor electronic circuit.

Next, the results of the comparative investigation of this example andrelated technology will be described. Examples of the related technologyinclude a method including disposing a throwaway pattern (dummy pattern)as well as an intrinsically necessary pattern in a wafer surface to beetched. An example in which such a throwaway pattern is disposed isdescribed in PTL 2. In a dry etching method and a thin film patternaccording to PTL 2, a pattern in which openings exist within 300 μm orless over the whole wafer surface is used when a silicon thin filmformed on a glass substrate is dry-etched. In addition, it is describedthat the etching of the whole wafer surface can be uniformalized. Whenthe related technology described above is applied as is to theproduction of a silicon optical waveguide, the following problem occurs.

FIG. 6A is a plan view of a semiconductor optical waveguide to which therelated dry etching method is applied, and FIG. 6B is a cross-sectionalview of the semiconductor optical waveguide. In a dummy semiconductorformed using the related technology, individual patterns areperiodically arranged over the whole wafer surface. In contrast, a corepattern forming a silicon optical waveguide structure 40 is arranged ata predetermined position in a wafer surface depending on the design ofan optical circuit. In periodically arranged dummy structures 30, dummypatterns (broken line portions of FIG. 6A) arranged in a regionoverlapping the silicon optical waveguide core pattern and in a regionin the vicinity of the silicon optical waveguide core pattern areremoved in advance in the stage of designing the optical circuit. Inthis case, a pattern obtained after the removal becomesline-asymmetrical with respect to the core central line of the opticalwaveguide.

The dummy patterns become line-asymmetrical with respect to the corecentral line, thereby allowing local etching regions in the vicinity ofthe optical waveguide core to be asymmetrical. Because a pattern densityin the wafer surface is kept at an approximately constant level due tothe arrangement of the dummy patterns, the average etching rate of thewhole wafer is kept at a constant level. However, in the vicinity of thewaveguide core, a local etching state is changed to change the shapes ofthe waveguide patterns from designed values. A problem occurs that it isimpossible to achieve desired properties in the optical waveguide inwhich a region requiring high processing accuracy is wide due to thedeviation of the shapes of the waveguide patterns from the designedvalues.

FIG. 7A is a plan view of another silicon optical waveguide to which therelated dry etching method is applied, and FIG. 7B is a cross-sectionalview of the silicon optical waveguide. In FIG. 7A and FIG. 7B, twosilicon optical waveguide patterns 40C and 40D in a silicon opticalwaveguide structure are arranged in the vicinity of each other. In aperiodically arranged dummy structure 30, dummy patterns arranged in aregion overlapping each optical waveguide pattern and in a region in thevicinity of each optical waveguide pattern are removed (broken lineportions of FIG. 7A). In this case, any dummy pattern is not arranged ina region between the two silicon optical waveguide patterns 40C and 40D.In other words, the dummy patterns are arranged only on the right of theoptical waveguide 40D. As a result, the dummy patterns are arrangedline-asymmetrically with respect to the core central line of the opticalwaveguide.

When the dummy patterns arranged in the optical waveguide region and theregion in the vicinity thereof are removed from the periodicallyarranged dummy patterns, and the remaining dummy patterns are arrangedasymmetrically with respect to the optical waveguide patterns, etchingregions in the right and left of the optical waveguide core becomesasymmetrical. In this case, a local etching state is changed in thevicinity of the waveguide core, and the shapes of the waveguide patternsdeviate from designed values. As a result, a problem occurs that it isimpossible to achieve desired properties in the optical waveguides inwhich it is necessary to control the optical phase of propagating lightwith high accuracy, and the like. In particular, this problem becomesremarkable when a plurality of optical waveguides are arranged inparallel.

As described above, it is impossible to actualize a silicon opticalwaveguide having desired properties that reflect design when dummypattern arrangement used in a step for dry-etching a relatedsemiconductor electronic circuit is applied as is to a process formanufacturing a silicon optical waveguide.

In contrast, in this exemplary embodiment, the symmetrical arrangementof the dummy patterns is maintained even in the region in the vicinityof the optical waveguide, as described above. In other words, theoptical waveguide pattern included in the silicon optical waveguidestructure has a line-symmetrical axis, and the dummy patterns arearranged line-symmetrically with respect to the optical waveguidepattern. Accordingly, using a process for manufacturing a semiconductorelectronic circuit, desired properties can be achieved even for anoptical waveguide in which a region requiring high processing accuracyis wide, and for an optical waveguide in which it is necessary tocontrol the optical phase of propagating light with high accuracy. Asdescribed above, this exemplary embodiment has excellent effects incomparison with the related technology.

Second Exemplary Embodiment

FIG. 2 is a plan view illustrating the configuration of a semiconductoroptical waveguide according to a second exemplary embodiment of thepresent invention. The configuration of the plan view illustrated inFIG. 2 and the configuration of the plan view illustrated in FIG. 1A aredifferent from each other in view of the shapes of dummy patternsarranged in a region with maintained symmetry. In other words, in FIG.2, a plurality of dummy patterns arranged in a region in the vicinity ofa silicon optical waveguide structure 40 have partially chipped shapes,thereby forming pseudo-lattice-shaped dummy structures 32. The otherconfiguration is formed in the same manner as in the semiconductoroptical waveguide of FIG. 1A.

In other words, the dummy patterns having the partially chipped shapesare arranged line-symmetrically with respect to the central line of thecore pattern of the silicon optical waveguide structure 40, asillustrated in FIG. 2. In this exemplary embodiment, the uniformity ofetching is also obtained by arranging the dummy patternsline-symmetrically in the region in the vicinity of an optical waveguidecore.

As described above, the dummy patterns arranged in the region in thevicinity of the optical waveguide may have the partially chipped shapesof the patterns. Due to the shapes and arrangement of such dummypatterns, the formation of the optical waveguide with high accuracy ismaintained in a process for etching an optical waveguide core. In otherwords, the semiconductor optical waveguide having desired properties canbe formed using a process for manufacturing a semiconductor electroniccircuit.

Third Exemplary Embodiment

FIG. 3 is a plan view illustrating the configuration of a semiconductoroptical waveguide according to a third exemplary embodiment of thepresent invention. The configuration of the plan view illustrated inFIG. 3 and the configuration of the plan view illustrated in FIG. 1A aredifferent from each other in view of the shapes of dummy patternsarranged in a region in the vicinity of a silicon optical waveguidestructure 40. In other words, in FIG. 3, dummy patterns forming dummystructures continue in the elongation direction of the core central lineof the semiconductor optical waveguide, and are not separated. The longdummy structures 33 are arranged line-symmetrically with respect to thecentral line of the core pattern of the silicon optical waveguidestructure 40. The other configuration is the same as the configurationillustrated in FIG. 1A.

For example, many bending patterns of an optical waveguide are generatedin the design of the downsizing and integration of the opticalwaveguide. When lattice-shaped dummy patterns are arranged in thevicinities of the right and left of the arc-shaped optical waveguidepatterns, a problem such as remaining of small patterns may occur in amanufacturing process. It is not necessary to arrange square-shapeddummy patterns in a lattice shape. In a region having a complicatedshape in which the dummy patterns and waveguide patterns overlap eachother, the dummy patterns can be arranged in such a way that the dummypatterns are formed to be long similarly in the case of the waveguidepatterns, and the density of the dummy patterns is constant.

As described above, dummy patterns at distances near to the core centerof a waveguide pattern more strongly affect the etching state of anoptical waveguide. Thus, for example, long dummy patterns can also bearranged within distances of up to around 60 μm from a waveguide corecenter, and lattice-shaped dummy patterns can also be arranged in aregion at not less than a distance of 60 μm. It is not necessary toarrange lattice-shaped dummy patterns in an outer regionline-symmetrically with respect to a core central line.

By arranging long dummy patterns, line symmetry with respect to the corecenter of the dummy patterns can be secured even in a bending waveguidedesigned in a complicated shape such as, for example, a trigonometricfunction or a clothoid curve, and the control of the optical phase ofguided light can be stabilized.

As described above, the dummy patterns arranged in the region in thevicinity of the optical waveguide can be formed by continuouslyarranging the individual patterns in the direction of the core centralline. By arranging such long dummy patterns, design with high accuracycan be maintained in an etching process. In other words, thesemiconductor optical waveguide having desired properties can beactualized using a process for manufacturing a semiconductor electroniccircuit.

Fourth Exemplary Embodiment

FIG. 4 is a plan view illustrating the configuration of a semiconductoroptical waveguide according to a fourth exemplary embodiment of thepresent invention. The configuration of the plan view illustrated inFIG. 4 and the configuration of the plan view illustrated in FIG. 1A aredifferent from each other in view of the number of optical waveguides,and a form for arranging the optical waveguides. In other words, thedistance between two silicon optical waveguide patterns 40A and 40Badjacent to each other varies in silicon optical waveguide structures ofFIG. 4. In FIG. 4, square-shaped dummy patterns are arranged in a regionbetween the two optical waveguide patterns 40A and 40B adjacent to eachother. The other configuration is the same as the configurationillustrated in FIG. 1A.

When a plurality of optical waveguide patterns are arranged in parallel,the design of optical phases with high accuracy, causing no opticalphase difference between the optical waveguides, may be demanded.However, when the distance between two optical waveguides is short, itis impossible to arrange the dummy patterns line-symmetrically withrespect to a core center in the individual optical waveguides. Thus, theplurality of optical waveguide patterns are regarded as one group, andthe dummy patterns are arranged to be line-symmetrical with respect tothe central line of the group (hereinafter referred to as “patterncentral line”). Although such an arrangement allows the core shapes ofthe individual optical waveguides to be changed in comparison with thecase of achieving symmetry with respect to a core central line as inFIG. 1A, the core shapes are similarly changed in two optical waveguidessymmetrically with respect to the pattern central line, and the changesof the optical phases are the same. In other words, the amounts ofchange in the optical phases between the plurality of optical waveguidesbecome equal due to symmetry, and no difference between the opticalphases occurs. Accordingly, performance can be prevented fromdeteriorating in an optical circuit using a relative phase differencesuch as an asymmetrical Mach-Zehnder interferometer.

As described above, a plurality of dummy patterns forming a dummystructure 35 in a region between the silicon optical waveguidestructures are also arranged line-symmetrically with respect to acentral line (pattern center) in the case of grouping the two opticalwaveguides 40A and 40B. As a result, the symmetry of the arrangement ofthe dummy patterns with respect to an optical waveguide core is kept,and an in-plane distribution is maintained in etching.

As described above, symmetry with respect to the central line of thegrouped optical waveguide patterns is maintained in a region in thevicinity of the region with the varying spacing between the two opticalwaveguide patterns adjacent to each other. As a result, design with highaccuracy can be maintained in a process for etching an optical waveguidecore. In addition, the semiconductor optical waveguide having desiredproperties can be actualized using a process for manufacturing asemiconductor electronic circuit.

Fifth Exemplary Embodiment

FIG. 5A is a plan view illustrating the configuration of a siliconoptical waveguide according to a fifth exemplary embodiment of thepresent invention, and FIG. 5B is a cross-sectional view of the siliconoptical waveguide. The configuration illustrated in FIG. 5A is differentfrom the configuration illustrated in FIG. 1A in that the siliconoptical waveguide is not a ridge type but a channel type. In otherwords, the cross-sectional shape of an optical waveguide core 20 is notthe projection shape of a ridge optical waveguide but the rectangularshape of a channel optical waveguide in the cross-sectional view of FIG.5B taken along the line B-B′ of FIG. 5A. In other words, in FIG. 5B,there are regions in which a lower silicon oxide layer 11 and an uppersilicon oxide layer 13 come in contact with each other. The otherconfiguration is the same as the configuration of FIG. 1.

In FIG. 5A and FIG. 5B, a plurality of dummy patterns forminglattice-shaped dummy structures are also arranged line-symmetricallywith respect to the core central line of a silicon optical waveguidestructure 40. As described above, the effect of decreasing the influenceof the position of the arrangement of the waveguide core and ofdecreasing the local in-plane distribution of etching is also exerted bymaintaining the arrangement symmetry of the dummy patterns with respectto the optical waveguide core, in this example.

The arrangement pattern according to this exemplary embodiment isapplicable not only to a linear optical waveguide pattern but also to apattern in an asymmetrical Mach-Zehnder interferometer, an arrayedwaveguide grating (AWG), an optical delay circuit, a grating, a ringresonator, an optical 90-degree hybrid mixer, or the like. Theapplication to the design of an optical waveguide in which the phasestate of guided light is important is possible, and can be expected toexhibit a similar effect.

The silicon optical waveguide may not be a ridge type but be a channeltype. The cross-sectional shapes of the dummy patterns may not beprojection shapes but be rectangular shapes. As described above, it ismade possible to maintain design with high accuracy in an etchingprocess by arranging the dummy patterns line-symmetrically with respectto the core central line or pattern central line of the opticalwaveguide pattern. As a result, the semiconductor optical waveguidehaving desired properties can be actualized using a process formanufacturing a semiconductor electronic circuit.

Some or all of the exemplary embodiments described above can bedescribed as the following supplementary notes, but are not limited tothe following.

(Supplementary Note 1)

A semiconductor optical waveguide, including:

a substrate;

a semiconductor optical waveguide structure arranged on the substrate;and

a semiconductor dummy structure arranged, apart from the semiconductoroptical waveguide structure, on the substrate,

wherein the semiconductor optical waveguide structure includes aline-symmetric pattern on a plane that is parallel to the substrate; and

-   -   the semiconductor dummy structure includes a region in which a        pattern shape on a plane that is parallel to the substrate is        symmetric with respect to the symmetry axis of the        line-symmetric pattern.

(Supplementary Note 2)

The semiconductor optical waveguide according to Supplementary Note 1,

wherein the pattern shape includes a periodic structure.

(Supplementary Note 3)

The semiconductor optical waveguide according to Supplementary Note 2,

wherein the pattern shape is in a state in which a part or the whole ofeach pattern forming the pattern shape is chipped in the vicinity of thesemiconductor optical waveguide structure.

(Supplementary Note 4)

The semiconductor optical waveguide according to Supplementary Note 3,wherein the vicinity includes a region in which the field distributionof guided light propagating through the semiconductor optical waveguidestructure exists.

(Supplementary Note 5)

The semiconductor optical waveguide according to any one ofSupplementary Notes 1 to 4,

wherein each pattern shape forming the semiconductor dummy structure isa rectangular shape.

(Supplementary Note 6)

The semiconductor optical waveguide according to any one ofSupplementary Notes 1 to 4,

wherein the pattern shape includes a region in which each pattern shapeforming the pattern shape continues in a direction along the symmetryaxis.

(Supplementary Note 7)

The semiconductor optical waveguide according to any one ofSupplementary Notes 1 to 6,

wherein in a case in which the shape of the semiconductor opticalwaveguide structure is a single linear shape, the symmetry axis is thecentral line of the linear shape.

(Supplementary Note 8)

The semiconductor optical waveguide according to any one ofSupplementary Notes 3 to 5,

wherein the semiconductor optical waveguide structure includes aplurality of optical waveguide structures; and

the pattern shape in the vicinity of a region between the plurality ofoptical waveguide structures includes at least one unit pattern formingthe pattern shape.

(Supplementary Note 9)

An optical communication device, including the semiconductor opticalwaveguide according to any one of Supplementary Notes 1 to 8.

(Supplementary Note 10)

A method for manufacturing a semiconductor optical waveguide, including:

a step of forming a mask pattern used when a semiconductor layer isetching-processed; and

a step of forming a semiconductor optical waveguide structure byetching-processing a semiconductor layer using the mask pattern,

wherein the step of forming the mask pattern includes steps of:

arranging a dummy structure pattern with a periodic structure on thewhole surface of a target region to be etching-processed;

forming an optical waveguide structure pattern with a line-symmetry axison the target region;

allowing the dummy structure pattern to overlap with the opticalwaveguide structure pattern in such a way that the dummy structurepattern is symmetrical with respect to the line-symmetry axis; and

removing the dummy structure pattern in the vicinity of the opticalwaveguide structure pattern.

This application claims priority based on Japanese Patent ApplicationNo. 2013-261096, which was filed on Dec. 18, 2013, and of which theentire disclosure is incorporated herein.

INDUSTRIAL APPLICABILITY

The semiconductor optical waveguide according to the present inventioncan be applied to optical communication devices of which the higherintegration, downsizing, higher functions, lower costs, and the like aredemanded.

REFERENCE SIGNS LIST

-   10 Silicon substrate-   11 Lower silicon oxide layer-   12 Silicon layer-   13 Upper silicon oxide layer-   20 Core-   21 Slab-   30 Dummy structure-   31 Dummy structure-   32 Dummy structure having pseudo-lattice shape-   33 Long dummy structure-   34 Removal trace of lattice-shaped dummy structure-   35 Dummy structure in region between silicon optical waveguide    structures-   40 Silicon optical waveguide structure-   40A, 40B, 40C, 40D Silicon optical waveguide pattern

1. A semiconductor optical waveguide, comprising: a substrate; asemiconductor optical waveguide structure arranged on the substrate; aplanar region formed around the semiconductor optical waveguidestructure on the substrate; and a semiconductor dummy structure that isarranged around the planar region on the substrate and is formed of aplurality of dummy patterns, wherein the semiconductor optical waveguidestructure comprises a line-symmetric pattern on a plane that is parallelto the substrate; and the plurality of dummy patterns are arrangedsymmetrically with respect to a symmetry axis of the line-symmetricpattern.
 2. The semiconductor optical waveguide according to claim 1,wherein the planar region comprises a field distribution of guided lightpropagating in the semiconductor optical waveguide.
 3. The semiconductoroptical waveguide according to claim 1, wherein the plurality of dummypatterns are arranged periodically.
 4. The semiconductor opticalwaveguide according to claim 3, wherein the semiconductor dummystructure is formed by arranging a plurality of dummy patterns withrectangular shapes in a lattice shape.
 5. The semiconductor opticalwaveguide according to claim 3, wherein the semiconductor dummystructure is formed by arranging, in a stripe shape, a plurality of longdummy patterns extending in a longitudinal direction of the symmetryaxis.
 6. The semiconductor optical waveguide according to claim 1,wherein a dummy pattern that comes in contact with the planar regioncomprises a shape of a partially cut dummy pattern that does not come incontact with the planar region.
 7. The semiconductor optical waveguideaccording to claim 1, comprising a plurality of semiconductor opticalwaveguides and a planar region, wherein the plurality of dummy patternsare arranged symmetrically with respect to a central line depending onthe plurality of semiconductor optical waveguides.
 8. The semiconductoroptical waveguide according to claim 1, further comprising a secondsemiconductor dummy structure that is arranged outside the semiconductordummy structure on the substrate, and is formed of a plurality of dummypatterns arranged at a predetermined density.
 9. An opticalcommunication device, comprising the semiconductor optical waveguideaccording to claim
 1. 10. A method for manufacturing a semiconductoroptical waveguide, comprising: arranging a first clad layer and a corelayer on a substrate; forming a core pattern by subjecting the corelayer to photolithography and etching using a predetermined mask; andarranging a second clad layer on the formed core pattern, wherein themask is formed by: periodically arranging a plurality of dummy patterns;removing a dummy pattern in a safety distance range with a predeterminedcentral axis as a center; rearranging a dummy pattern in a controlregion that is adjacent to an outside of the safety distance rangeline-symmetrically with respect to the central axis; and forming anoptical waveguide structure pattern in the safety distance range in sucha way that the central axis and a central line of the optical waveguidestructure pattern coincide with each other.
 11. The semiconductoroptical waveguide according to claim 2, wherein the plurality of dummypatterns are arranged periodically.
 12. The semiconductor opticalwaveguide according to claim 11, wherein the semiconductor dummystructure is formed by arranging a plurality of dummy patterns withrectangular shapes in a lattice shape.
 13. The semiconductor opticalwaveguide according to claim 11, wherein the semiconductor dummystructure is formed by arranging, in a stripe shape, a plurality of longdummy patterns extending in a longitudinal direction of the symmetryaxis.
 14. The semiconductor optical waveguide according to claim 2,wherein a dummy pattern that comes in contact with the planar regioncomprises a shape of a partially cut dummy pattern that does not come incontact with the planar region.
 15. The semiconductor optical waveguideaccording to claim 3, wherein a dummy pattern that comes in contact withthe planar region comprises a shape of a partially cut dummy patternthat does not come in contact with the planar region.
 16. Thesemiconductor optical waveguide according to claim 2, comprising aplurality of semiconductor optical waveguides and a planar region,wherein the plurality of dummy patterns are arranged symmetrically withrespect to a central line depending on the plurality of semiconductoroptical waveguides.
 17. The semiconductor optical waveguide according toclaim 3, comprising a plurality of semiconductor optical waveguides anda planar region, wherein the plurality of dummy patterns are arrangedsymmetrically with respect to a central line depending on the pluralityof semiconductor optical waveguides.
 18. The semiconductor opticalwaveguide according to claim 2, further comprising a secondsemiconductor dummy structure that is arranged outside the semiconductordummy structure on the substrate, and is formed of a plurality of dummypatterns arranged at a predetermined density.
 19. The semiconductoroptical waveguide according to claim 3, further comprising a secondsemiconductor dummy structure that is arranged outside the semiconductordummy structure on the substrate, and is formed of a plurality of dummypatterns arranged at a predetermined density.